It is known to apply concrete surface retarders onto the inner surfaces of moulds or formworks (which are essentially large-scale moulds of assembled wooden boards or shuttering for making walls, foundations, etc.), and exposing the aggregates at the surface of the moulded concrete shape or article. It is customary for commercial “in form” concrete surface retarder products to be provided in the form of solvent-based compositions. These products are typically sprayed or rolled onto the inner surfaces of the concrete mould or formwork.
The cement paste portion of the concrete, which has been in contact with the surface retarder coating, can be removed through the use of pressurized water (spray) to expose aggregates that are embedded in the concrete beneath its removed surface. Most of the commonly used mould-release surface retarders incorporate solvents for their quick drying characteristics. However, solvents generate environmental, health, and safety issues, and hence are subject in many countries to stringent regulation. Manufacturers have attempted to replace solvents with water-based products for these reasons. However, water-based formulations have longer relative drying times compared to solvent-based formulations,
Many precast operations take place in open, unheated areas, and these are not favorable conditions for achieving quick trying times when using conventional water-based products, because rate of water evaporation is considerably impeded. This condition is particularly noticeable in the winter time, when temperatures are low and the relative humidity is high on account of the wet concrete environment. Precast concrete panel manufacturers, for example, must plan the application of water-based surface retarder products very early in the day. Concrete panels often must be heated within the formwork to reduce drying time so that at least one concrete panel can be produced from the formwork for each day of operation.
In World Patent Application No. WO 2002/003448 of Grace Construction Products, a method is disclosed for increasing productivity levels without relying on harmful solvents. In this method, a hot melt coating composition containing surface retarder actives is spray-applied onto concrete or onto the surfaces of a concrete mould. However, this approach requires much more robust equipment than is the case for typical spray application of a water- or solvent-based surface retarder-coating composition. It would therefore appear to be an economically feasible opportunity for only the largest precast businesses to pursue.
Accordingly, a novel composition and process are needed for achieving high productivity in cement and concrete moulding operations wherein surface retarders are applied to formworks without the use of solvent-containing products that release volatile organic chemicals (VOCs) into the environment.